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<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body></body>
</html>
<script>
  // A-Z:65-90
  // a-z:97-122
  function rot13(str) {
    let Str = "";
    for (let i = 0; i < str.length; i++) {
      let code = str.charCodeAt(i);
      if (code >= 65 && code <= 90) {
        code += 13;
        if (code > 90) {
          code -= 26;
        }
      } else if (code >= 97 && code <= 122) {
        code += 13;
        if (code > 122) {
          code -= 26;
        }
      }
      Str += String.fromCharCode(code);
    }
    //
    console.log(Str);
  }

  rot13("SERR CVMMN!");
</script>
